public class MultithreadedFocusTrackingIterator extends FocusTrackingIterator
FocusTrackingIterator
. It is identical
to the superclass except that the methods are synchronized. It is used when there is any possibility
that the iterator will be used from multiple threads.
The class is not designed to allow arbitrary multi-threaded operation. For example, one thread
might exhaust the input after another thread has called hasNext()
, causing the first thread
to get no results from a call of next()
. Instead, the synchronization is designed only to
allow a call on getLength()
(caused by an XPath invocation of last()
) to occur
asynchronously with the thread that advances the iterator. This happens specifically when an
xsl:result-document
instruction is executed asynchronously, and the code within
the body of the xsl:result-document
instruction calls last()
. In this situation
the main thread (the one that advances the focus, and spawns new threads for xsl:result-document
)
must be suspended while the value of last()
is computed, which is done by reading the iterator
to completion; when the main thread resumes, there will be a new base iterator positioned over the materialized
sequence that was read into memory as a side-effect of calling last()
.
See bug 3927.
Constructor and Description |
---|
MultithreadedFocusTrackingIterator(SequenceIterator base) |
Modifier and Type | Method and Description |
---|---|
void |
close()
Close the iterator.
|
Item |
current()
Get the current value in the sequence (the one returned by the
most recent call on next()).
|
int |
getLength()
Get the position of the last item in the sequence.
|
GroundedValue |
getResidue()
Return a GroundedValue containing all the remaining items in the sequence returned by this
SequenceIterator, starting at the current position.
|
int |
getSiblingPosition(NodeInfo node,
NodeTest nodeTest,
int max)
Get the sibling position of a node: specifically, count how many preceding siblings
of a node satisfy the nodetest.
|
SequenceIterator |
getUnderlyingIterator()
Get the underlying iterator
|
boolean |
hasNext()
Determine whether there are more items to come.
|
GroundedValue |
materialize()
Return a GroundedValue containing all the items in the sequence returned by this
SequenceIterator.
|
Item |
next()
Get the next item in the sequence.
|
int |
position()
Get the current position.
|
boolean |
supportsGetLength()
Ask whether this iterator supports use of the
FocusTrackingIterator.getLength() method. |
discharge, isActuallyGrounded, supportsHasNext, track
public MultithreadedFocusTrackingIterator(SequenceIterator base)
public SequenceIterator getUnderlyingIterator()
getUnderlyingIterator
in class FocusTrackingIterator
public Item next()
next
in interface SequenceIterator
next
in class FocusTrackingIterator
public Item current()
current
in interface FocusIterator
current
in class FocusTrackingIterator
public int position()
This method does not change the state of the iterator.
position
in interface FocusIterator
position
in class FocusTrackingIterator
public boolean supportsGetLength()
FocusTrackingIterator
FocusTrackingIterator.getLength()
method. This
method should always be called before calling FocusTrackingIterator.getLength()
, because an iterator
that implements this interface may support use of FocusTrackingIterator.getLength()
in some situations
and not in otherssupportsGetLength
in interface LastPositionFinder
supportsGetLength
in class FocusTrackingIterator
FocusTrackingIterator.getLength()
method can be called to determine the length
of the underlying sequence.public int getLength()
getLength
in interface LastPositionFinder
getLength
in interface FocusIterator
getLength
in class FocusTrackingIterator
public boolean hasNext()
This method must not be called unless the result of FocusTrackingIterator.supportsHasNext()
is true.
hasNext
in interface LookaheadIterator
hasNext
in class FocusTrackingIterator
java.lang.ClassCastException
- if the base iterator does not support lookahead processingpublic GroundedValue materialize()
materialize
in interface GroundedIterator
materialize
in class FocusTrackingIterator
UncheckedXPathException
- in the cases of subclasses (such as the iterator over a MemoClosure)
which cause evaluation of expressions while materializing the value.public GroundedValue getResidue()
getResidue
in interface GroundedIterator
getResidue
in class FocusTrackingIterator
UncheckedXPathException
- in the cases of subclasses (such as the iterator over a MemoClosure)
which cause evaluation of expressions while materializing the value.public void close()
(Currently, closing an iterator is important only when the data is being "pushed" in another thread. Closing the iterator terminates that thread and means that it needs to do no additional work. Indeed, failing to close the iterator may cause the push thread to hang waiting for the buffer to be emptied.)
close
in interface java.io.Closeable
close
in interface java.lang.AutoCloseable
close
in interface SequenceIterator
close
in class FocusTrackingIterator
public int getSiblingPosition(NodeInfo node, NodeTest nodeTest, int max)
xsl:apply-templates
select="*"
(which selects a set of sibling nodes) is used in conjunction with patterns
such as match="*[position() mod 2 = 1]
, then calculation of the position of one
node in the sequence of siblings can take advantage of the fact that the position of the
immediately preceding sibling is already known.
This optimization was suggested by the late Sebastian Rahtz, one of Saxon's earliest power users, and it is dedicated to his memory.
getSiblingPosition
in class FocusTrackingIterator
node
- the starting node, which is assumed to satisfy the node testnodeTest
- the node testmax
- the maximum number of nodes to be countedCopyright (c) 2004-2022 Saxonica Limited. All rights reserved.